Integrated circuits (ICs) can be damaged by electrostatic discharge (ESD). For example, ESD can damage a gate oxide of a transistor. To protect the transistor from damage, an ESD protection circuit is used to dissipate ESD current through the substrate of the IC. When a static discharge is detected at a pad of an IC, the ESD circuit is activated to dissipate current through the substrate, protecting the gate oxide.
Various types of ESD protection circuit have been used. One type of ESD protection circuit is a lateral diffused metal oxide semiconductor (LDMOS) transistor. The thermal runaway current (e.g., It2) which relates to the ESD performance of the LDMOS is directly related to its total width. For example, the larger the total width of LDMOS transistor, the higher the It2. However, conventional LDMOS transistors exhibit non-uniformity of the relationship between width and It2. For example, increasing the total width of a LDMOS transistor does not result in the expected increase in It2. In some instances, increasing the total width of the LDMOS transistor results in a decrease in It2. Such non-uniformity negatively impacts ESD design rules, making it difficult for IC designers to provide the necessary ESD protection.
The disclosure is directed to provide improved uniformity in LDMOS transistors.